Conventional wet-process manufacturing of phosphoric acid, such as for fertilizer production, sets up extensive acidic water cooling ponds, which pollute the environment with residual phosphoric acid and also with fluorine-containing gases and other contaminants.
Attempts to limit the resulting contamination have had degrees of success, but acceptance of the ponds has precluded comprehensive treatment of the underlying pollution problem--and fundamentally has precluded its satisfactory resolution. In other words, for the most part the attempts have been constrained by self-limiting conditions. Examples include treatment of acid pond waters to remove metallic ions as in Mills U.S. Pat. No. 4,303,532; to recover calcium fluoride as in Hirka & Mills U.S. Pat. No. 4,171,342 or O'Neill U.S. Pat. No. 4,374,810; or to remove calcium fluoride so as to provide a reduced fluoride solution for use in wet ball-milling of phosphate rock as in O'Neill et al. U.S. Pat. No. 4,472,368.
Palm and Hartig undertook to neutralize such acid pond waters, as in U.S. Pat. No. 4,320,012. The present invention is so directed as to retain the benefits of that contribution while further minimizing pollution attributable to wet-process phosphoric acid production.